The present invention relates to a prosthetic knee joint and is specifically directed to one which permits functional motion including some rotational movement as the knee moves from flexion to extension and vice-versa. It is particularly well-suited where deterioration of the tissues of the knee joint require augmentation or substitution of the medial and/or lateral collateral ligaments and in cases where there is global instability, bony and ligaments deficiencies or dysfunction.
The development of knee prostheses involves a multitude of factors which must be taken into consideration due to the complexity of the knee. A balancing of such factors is required in order to design a knee prosthesis which provides the necessary support and range of motion over an extended number of years with while maintaining optimal function. It is desirable to remove as little bone as possible and to preserve as much of the soft tissue as possible; however, deterioration from disease or other causes can require extensive removal of bone and augmentation or substitution of the deficient ligaments and other soft tissue.
There is shown in the prior art a variety of types of knee joint prostheses designed to accommodate various specific problems and various amounts of bone removal depending upon the condition of the patient. For example, U.S. Pat. No. 4,301,553, incorporated herein by reference, is directed to a hinged knee joint which is intended to perform in an almost natural anatomical manner utilizing a hinged coupling which is pivotally attached to a flanged stem element having a rod depending thereon and permitting the joint to undergo relative rotation in at least two planes while distributing load forces over substantial bearing areas.
U.S. Pat. No. 3,996,624 discloses another type of prosthetic knee joint having a shaft rotatably mounted in the openings in the condyloid elements of the femoral prosthesis and extending through a hole in the center portion of the tibial prosthesis and is designed utilizing configurations and materials for the respective components to insure that normal wear associated with the bearing surfaces does not change the relative centers of the rotating surfaces and thereby does not introduce excentricity in the concentric bearing system.
U.S. Pat. No. 4,634,444 discloses a knee joint having bearing surfaces of large areas, while U.S. Pat. No. 5,011,496 discloses a prosthetic joint which provides a large area of contact between the bearing surfaces as the knee is flexed while permitting posterior movement of the femoral component relative to the tibial component during flexing. One embodiment of such patent also discloses a constrained or hinged prosthesis.
U.S. Pat. No. 4,714,475 discloses a tibial member of a knee joint endoprosthesis in which an artificial tendon of appropriate plastic material is utilized to secure a patella to a tibial endoprosthesis by fastening ends of the natural tendons of the patella which were severed as part of a resectioning process to such tibial endoprosthesis.
U.S. Pat. No. 3,745,590 relates to an articulating prosthesis which uses a synthetic flexible ligamentous attachment to fasten a shaped thumb joint prosthesis to an adjacent tendon, ligament or bone.
U.K. Patent Specification 1,603,833 discloses a prosthetic knee joint device having elongate flexible members connected under tension between first and second components connected to the upper and lower limb portions of an artificial leg.
Zimmer, Inc. 1981 catalog shows an OFFSET HINGE.TM. total knee designed for use whenever instability of the knee joint exists due to the absence of cruciate and/or collateral ligaments.
Catalog entitled "The Howmedica.RTM. Kinematic.TM. Knee System" discloses four knee prosthesis systems including one entitled "The Kinematic Rotating Hinge" having an anatomically similar rotational axis hinge permitting rotational laxity about the tibial axis to reduce stresses at the bone-cement interfaces.